This invention relates to pipe swivel joints, and more particularly to swivel joints designed especially for use on marine loading arms. Patents on apparatus of this type can be found in class 137, subclass 615, class 141, subclass 387, and various subclasses of class 285 of the classification of United States Patents.
Transferring petroleum and other fluid cargo between a reservoir facility and a marine tanker requires the use of a non-rigid connection between the reservoir and the tanker in order to compensate for movement of the tanker in response to tide, currents, wind, and the change in cargo level. The most satisfactory apparatus for this purpose is a marine loading arm, a crane-like device comprising a plurality of fluid-conducting pipe booms interconnected by swivel joints and counterbalanced on a vertical support called a riser, the riser being connected to a reservoir facility and the outer or distal end of the outermost pipe boom having a triple-swivel joint assembly with an end flange for connecting the arm to the manifold flange of the tanker. Devices of this type are illustrated and described in Bily U.S. Pat. No. 3,382,893 issued on May 14, 1968, and the contents thereof are expressly incorporated herein by reference.
One of the problems associated with the use of some styles of loading arms is the effort required to maneuver the arm's end flange into position for connecting it to the tanker's vertical manifold flange. When at rest the arm's end flange normally resides in a somewhat downwardly-facing attitude, i.e., at an angle between horizontal and vertical, and thus must be raised into coupling position. Usually this is done by hand, but often the combined weight of the flange and that portion of the triple-swivel coupling assembly that must be lifted is too much for a man to overcome, especially where the larger arms, such as those with pipes of sixteen to twenty-four inches in diameter, are involved. Although some triple-swivel assemblies are configured so that the end flange when at rest is disposed in a vertical attitude, the extra pipe elbows required to accomplish this attitude not only increase the cost but also impose a considerable amount of moment load on the arm, thereby requiring the use of heavier counterweights and proportionately larger supporting elements. Thus, the standard triple-swivel assembly such as that described in the foregoing Bily patent, is still preferred for many installations, and any reduction in the angle from the vertical at which its end flange resides comprises a valuable improvement in the ease with which this type of assembly can be utilized.
Another problem associated with the standard triple-swivel assembly is that the packing between the relatively rotatable elements of the swivel joints is often both difficult and time consuming to service or replace. This is particularly true when the assembly is of large diameter and therefore very heavy, and especially when the swivel joint must be completely disassembled in order to obtain access to its packing chambers.